Two coloring methods are usually used for the color-changing treatment of keratin fibers. By the first method, the coloring is accomplished with oxidative or permanent colorants by use of a mixture of different developers and couplers and of an oxidant. By this method, if necessary, it is possible to add a direct (non-oxidative) dye if the coloring result is to be adjusted or special coloring effects are to be achieved. The second method involves the exclusive use of direct dyes which in an appropriate carrier composition are applied to the fibers. This method is easy to apply, very gentle and causes only minor damage to the keratin fibers. The direct dyes used for this purpose are subject to many requirements. For example, they must be unobjectionable from a toxicological and dermatological standpoint and they must make it possible to attain colorations of a desired intensity which, among other things, presupposes sufficient water solubility. Moreover, the colorations obtained must exhibit good light stability, acid resistance and abrasion resistance.
Compared to oxidative colorations, however, non-oxidative ones as a rule are less durable and exhibit a less adequate color balance. In addition, direct dyes usually are not capable of “imparting to the hair a brighter shade”, because many direct dyes do not tolerate the oxidants needed for brightening and/or the required pH which is higher than or equal to 9.